Mediating effect of telomere length on relationship between lead and cadmium coexposure and blood glucose

Background Individual lead or cadmium exposure can cause abnormal blood glucose level and changes in telomere length, and the role of telomere length in the relationship between heavy metal joint exposure and blood glucose level is still unclear.

Objective To explore the role of telomere length in the relationship between lead and cadmium coexposure and blood glucose.

Methods A cross-sectional study was conducted. By convenient sampling method, 600 residents living in two communities in a city in North China were selected as participants from April to June 2016. Face-to-face interviews were performed to collect general demographics and lifestyles of the participants. The peripheral blood samples of the participants were collected for blood glucose and telomere length detection, the urine samples were collected for urinary cadmium, urinary lead, and urinary creatinine measurement, and both urinary cadmium and urinary lead were corrected by urinary creatinine. The included participants were divided into a control group, a high-cadmium and low-lead group, a high-lead and low-cadmium group, and a high-lead and high-cadmium group, according to the median levels of urinary cadmium and urinary lead. A restricted cubic spline model was constructed to analyze the relationship between urinary lead/cadmium levels and blood glucose concentrations in the four groups and the relationship between cadmium exposure and telomere length in the high-lead and high-cadmium group. Intermediary model test was conducted to analyze the effect of telomere length on the relationship between exposures to lead and cadmium and blood glucose.

Results The included participants were divided into the control group (n=99), the high-cadmium and low-lead group (n=91), the high-lead and low-cadmium group (n=145), and the high-lead and high-cadmium group (n=265). The differences in age, education level, per capita monthly household income, smoking, blood glucose, and telomere length were statistically significant among the four groups (P＜0.05). The high-lead and high-cadmium group had the highest blood glucose concentration, (5.63±1.68) mmol·L⁻¹, and the shortest telomere length, (2.63±1.05) Kb. The restricted cubic spline results showed that urinary cadmium level was correlated with blood glucose concentration in the high-lead and high-cadmium group (F=3.45, P=0.037), and there was a non-linear association (F=6.91, P=0.002); the association between urinary cadmium level and telomere length was also non-linear (F=5.93, P=0.043). The intermediary model test results showed that telomere length was a mediating variable between urinary cadmium level and blood glucose concentration, and the mediating effect size was 0.0192 (95%CI: 0.0007-0.0563), with a mediation ratio of 15.57%.

Conclusion Correlations between urinary cadmium and blood glucose and between urinary cadmium and telomere length were observed in the high-lead and high-cadmium coexposure group, and telomere length may play a mediating role in the relationship between them.